Consolidated Investment Products (Narrative) (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) entity	Dec. 31, 2019 USD ($) entity
Variable Interest Entity [Line Items]
Number of deconsolidated VIEs | entity	15	6
Number of deconsolidated VOEs | entity	11	11
Net impact on Consolidated Statements of Income	$ 0	$ 0
LIBOR spread on bank loan investments (percent)	11.00%
Percentage of collateral in default (percent)	1.17%	0.08%
Issued notes weighted average maturity period	10 years
Pre-defined spreads on variable rate notes - minimum (percent)	0.40%
Pre-defined spreads on variable rate notes - maximum (percent)	8.07%
Investments of CIP	$ 7,910,000,000.0	$ 7,808,000,000.0
Consolidated VIEs
Variable Interest Entity [Line Items]
Number of consolidated VIEs | entity	4	4
Number of consolidated VOEs | entity	2	5
Investments of CIP	$ 114,200,000	$ 508,700,000
Deconsolidated VIEs
Variable Interest Entity [Line Items]
Carrying value and maximum risk of loss with respect to VIEs	152,000,000.0	188,000,000.0
Investments of CIP	373,700,000	626,100,000
Senior secured bank loans and bonds
Variable Interest Entity [Line Items]
Bank loan investments	6,844,300,000	6,464,300,000
Excess of unpaid principal balances over fair value of senior secured bank loans and bonds	$ 208,600,000	181,200,000
Minimum
Variable Interest Entity [Line Items]
General term of partnerships	7 years
Maximum
Variable Interest Entity [Line Items]
General term of partnerships	12 years
Significant Unobservable Inputs (Level 3)
Variable Interest Entity [Line Items]
Investments of CIP	$ 0	$ 78,600,000